Well, I am biased towards the Colombian Bci, but I do own carpets as well - both are equally attractive snakes. I have found my boas to be calmer than my carpets in regards to being handled, though the carpets acclimate to it quickly enough. However my carpets are much more active overall than my boas, both in their cages and while being handled. My carpets rarely simply rest in my hands when I have them out but instead are exploring constantly. My boas are more prone to settle down on a warm lap and be still after the initial exploring session.
Depending on where you are located, there may be a reptile show coming up where you could look at several animals in person versus ordering online. Also prices tend to be better at shows and you may just be able to pick up both at the same time.
The season is upon us when you will find many more baby boas offered as well - generally starting in April, but I saw some newborns just this past weekend at my local show (northern Virginia). Whichever route you choose in purchasing, be sure to get the healthiest animal you can. If you buy online, go with someone reputable. If you purchase at a show, look the animal over carefully for any signs of parasites or disease. Obvious advise, I know, but bears repeating.
Good luck!
Raven